I've kinda' forgot right at this moment, but I want to say it very much can? If not necessarily has to in all situations.
There's tax relief available for certain kinds of debt, and certain ways of moving debt that count as income for purposes of taxation, just off the top of my head.
Think there's a few kinds that don't have to be reported (either at all, or in a yearly sense) by the person owing the debt (whoever they're paying is a different story, mind, and a thorough investigation would be subpoenaing those records as well), too, though, and gods only know how it varies on a state level, which is very much somethin' you'd be looking at when auditing along with whatever's part of the federal's purview.
E: Or to put it another way, even if it didn't the signs of it would. So it would only remain hidden if your books are cooked ridiculously well or the investigators involved are not terribly good at their job.
E2: Though... point the second (or third, or something), it's also very much possible he could be in massive debt, but not in a way that's abnormal. There's a lot of high roller stuff that can regularly be in debt for amounts approaching their net worth; in a financial sense it's even approaching optimal for certain industries. So massive debt could be just kinda' what should be there. It would proooobably still look absolutely terrible to huge chunks of the public, though, because gods know fiscal sensibility isn't terribly high up on our electorate's competencies or sense of priorities.